This invention relates to the use of a valve cutter for preparing a vein in situ for an arterial bypass.
Revascularization of lower limbs threatened by ischemia has long presented a challenge for vascular surgeons. Any obstruction of the inflow of arterial blood to the lower limbs, e.g. by the narrowing of arteries by spasm or disease, presents an immediate limb threatening condition where if not reversed can ultimately lead to amputation. Various surgical techniques have been devised to bypass the damaged or obstructed artery in order to restore lower limb circulation. A brief survey of the surgical procedures presently available will serve to highlight the limitations of the current techniques.
Historically, the use of infrapopliteal arteries as outflow tracts for bypassing occluded proximal arteries has become a well-established surgical entity. The use of the saphenous vein in situ as a conduit for bypassing nonfunctional arteries is a theoretical ideal since it provides viable, untraumatized endothelium and closely matches the size of the artery to be bypassed therefore facilitating anastomosis. Moreover, its gradual taper results in optimum flow characteristics. However, the chief obstacle in directing the flow of blood in veins from the heart to the limbs is the presence of valves in the veins. Venous valves are so arranged that they allow free passage of blood toward the heart but impede or prevent passage of blood in the opposite direction. Most commonly, each valve is composed of two leaflets placed opposite each other and when a current of blood or fluid away from the heart occurs, their opposed edges are brought together and the current is interrupted. In order to obliterate the functioning of the venous valves, several procedures have been devised: excising a segment of the vein and reversing its position; using a vein prosthesis constructed of synthetic material; and removal or destruction of the venous valves. In actual practice all of the above have been attempted with varying degrees of success.
The first of the above procedures to be tried was excision and reversal of the saphenous vein. The technique remains the one most commonly used and the standard against which alternatives are measured. Meticulous preservation of the endothelial lining of the veins harvested during vascular surgery is undoubtedly one of the most important factors in determining patency rates following bypass procedures. The vein wall is extremely sensitive to such factors as handling, toxic chemicals, cessation of blood flow and reacts to most local stimuli by undergoing vigorous and prolonged contractions. In spite of strict attention to details of vein harvesting, preparation and storage, endothelium desquamation occurs within a few minutes. Ultimate recovery of this endothelium may take up to 24 weeks. The patency rate of excised and reversed vein grafts falls sharply in the first 6-12 months, probably a direct consequence of early endothelium damage.
The quest for an autogenous tube lined with normal endothelium led to the concept of using the saphenous vein in situ. Fracture of the venous valve was one of the first attempts to destroy the functioning of the valves. This technique, originally suggested and used over 20 years ago, produced inconsistent results, the best of which were no better than those obtained with saphenous vein reversal. This eventually led to its virtual abandonment by 1970.
The use of synthetic vein prostheses has met with controversy. Dacron was first used in the early attempts but was abandoned quickly because of a prohibitive failure rate in the femoro-popliteal position. Subsequent use of newer nonautogenous materials, e.g. polytetrafluoroethylene, has been reported, but again with unpredictable and even diametrically opposed results. The use of a vein prosthesis has one distinct albeit limited advantage and that is for the patient not having a healthy saphenous vein available for bypass. This, however, occurs infrequently in the patients that present for arterial bypass.
A method known as valve excision was developed about the same time valve fracture was being attempted. Valve excision produced consistently good results but for a variety of reasons never gained acceptance in the United States.
The concept of valve incision, the surgical technique for which the present invention was designed, was developed by this inventor in 1974 primarily as a means for preparing the saphenous vein for its use in situ as an arterial bypass. In principle, the preparation of the saphenous vein for such use entails removal of the valvular obstructions to distal arterial flow, interruption of the venous branches which become arteriovenous fistulae when the vein is arterialized and the mobilization of its ends for construction of the proximal and distal arterial anastomoses. The technical objective is to accomplish this with the minimum of operative manipulation. It has been found that the simplest, most expedient and least traumatic method of rendering the bicuspid venous valve incompetent is to cut the leaflets in their major axes while they are held in the functionally closed position by fluid flow or arterial pressure from above. This is the essence of the technique of valve incision.
Valve incision as it was performed prior to this invention involved introducing scissors of varying length through a proximal incision of the saphenous vein, closing the valve leaflets with an influx of fluid and then cutting the leaflets with the scissors. Valves down as far as the midthigh were incised by this route. The remainder of the valves were most readily incised by the use of a valvulotome which cuts each leaflet successively by retrograde passage through the distal incision. The in situ method appears to be ideal because of the superior stability of the endothelium and vein wall throughout the procedure.
The currently available instruments for accomplishing valve incision are of two main types, (1) scissors with blunted tips and a narrow shank and (2) valvulotomes. Several limitations are associated with the use of each type.
Visualization of the valve site is mandatory when either the scissors or valvulotomes are used since each instrument can be readily but accidentally introduced into the side branches which are present at all valve sites causing subsequent laceration of the vein wall. Visualizing each valve site during surgery can be very time consuming. The longer a vein is deprived of its blood supply, the higher the risk of endothelial damage. Therefore, time is of the essence.
Also, limited access is encountered with each of the above instrument types. The blunted tipped scissors can only extend from the proximal vein incision to about midthigh. The remainder of the valves must be incised by inserting the valvulotome through a suitably placed side branch or through a puncture produced distal to the valve site. This may entail numerous punctures along the vein wall with a resulting concomitant increase in potential trauma sites. The above methods are tedious, time-consuming, and demanding of superior surgical skills, thus severely limiting the use of the saphenous vein in situ. The use of my valve cutter, hereinafter described, is simple and less demanding of time and skill.
The aforementioned limitations led to the development of this invention. The valve cutter that is used for incision of valve leaflets is made of nontoxic and inert material. Its component parts include a leader sufficiently rounded as to prevent damage to the vein wall, a cutting blade that is enclosed in a protective support that is also tapered in order to facilitate passage up and down the inside of the vein without damaging the endothelium and a torsionally rigid, but flexible rod that connects the leader to the cutting blade. A first aperture is located in the leader that provides an attachment site for an extension rod that is used for orienting the position of the valve cutter while inside the vein. A second aperture is located in the cutting blade support that permits suturing of the valve cutter to a catheter which serves as a conduit for the influx of fluid into the vein during the actual cutting procedure. The pressure of this fluid forces the valve leaflets into a closed position so that the leaflets can be efficiently engaged by the cutting blade.
The method for using the valve cutter involves exposing both proximal and distal sites of the vein and artery to be used for the bypass. A proximal incision is made into the vein and the first two valves are cut with blunted tipped scissors while they are held in the closed position. A distal incision is made and a rod is inserted up the vein until it exits at the proximal incision site. The valve cutter is attached to the rod and the entire unit is then pulled down the vein. The fluid from the catheter keeps the valve leaflets closed during the cutting procedure. The valve cutter assembly is then returned to the proximal incision, the valve cutter is dismounted and the rod is removed from the distal incision. The remaining distal valves are severed by using a valvulotome inserted either through the distal incision or vein side branches.
The design of my valve cutter for the above procedure has the following advantages: visualization of each valve site is no longer necessary; there is little risk of accidentally introducing the valve cutter into the venal side branches and risking laceration; there is little risk of lacerating the vein wall; and no significant shearing or frictional forces are placed on the extremely sensitive endothelium. Most importantly, this invention permits use of the saphenous vein in situ in a great number of cases where that is not now possible. As a result, it can be expected that an increased number of successful revascularizations of lower limbs threatened by ischemia will result with a consequent improvement in limb salvage rates.